IPTV (Internet Protocol Television) is a system where a digital television service is delivered using the Internet Protocol over a network infrastructure, which may include delivery by a broadband connection. Video content is typically compressed (i.e. the quantity of data used to represent the video content is reduced without an excessive reduction in quality) and then sent in a transport stream delivered via IP Multicast in case of live TV video content or via IP Unicast in case of Video on Demand (VOD) content.
Users of an IPTV service may have a personal video recorder (PVR)—a device that records video without videotape to a hard disk drive-based digital storage medium. Many PVRs are configured to receive two audio/video streams allowing users to view one of the A/V streams whilst recording the other A/V stream. In addition to recording without videotape, PVRs provide an end user with the functionality to fast forward, rewind and pause the video; the ability to instantly jump to any part of the video without having to rewind or fast forward the data stream; and often the ability to pause live video and start viewing video before the recording has finished. Commonly the hard drive forms part of a set top box (STB) that is connected to a display device such as a television. However, there is a very large number of STBs that have been deployed without hard drives leaving the users of such STBs without the PVR functionality described above.
A network personal video recorder (nPVR) has similar functionality to that of a PVR except that it stores video content on a network server instead of a local hard disk thus giving users of STBs deployed without hard drives the PVR functionality described above.
It is common for IPTV video content to be encrypted (obscured to make it unreadable without some special knowledge; sometimes referred to as scrambled). The control words used to encrypt the video are typically inserted into entitlement control message (ECM) packets and these ECMs are delivered to a STB as part of the video transport stream or on a separate port within the same multicast on which the transport stream is delivered.
U.S. Pat. No. 6,587,561 B1 describes a key delivery method for use in an encoded communications system in which at least one encoded item including a first item encoded with a first item control word is sent in a communication stream from a sender to a receiver, the method including transmitting an item entitlement control message (IECM) including item control information, transmitting a stream entitlement control message (SECM) including stream control information, and combining at least part of the item control information and at least part of the stream control information to produce the first item control word.
The disclosures of all references mentioned above and throughout the present specification, as well as the disclosures of all references mentioned in those references, are hereby incorporated herein by reference.